Wikipedia says "Evidence suggests that microbial metabolism may have contributed...

		pbhjpbhj on Sept 16, 2012 \| parent \| context \| favorite \| on: NASA Mars Rover Opportunity Reveals Geological Mys... Wikipedia says "Evidence suggests that microbial metabolism may have contributed to the formation of some of these concretions". Yet you state it as fact that these forms "are the byproduct of a type of bacteria" [my emphasis]. How come you're so certain?